1. Field of the Invention
The present invention relates to a laser apparatus, an exposure apparatus, a lithography system, and a method for producing circuit elements. In particular, the present invention relates to a laser apparatus based on the use of a mixed gas as a laser medium, an exposure apparatus and a lithography system for printing a fine pattern on a resist on a substrate such as a wafer by using a laser beam radiated from the laser apparatus, and a method for producing circuit elements comprising a lithography step of performing projection exposure with a mask pattern by using, as an exposure light beam, a light beam radiated from a laser beam source based on the use of a mixed gas as a laser medium. The laser apparatus according to the present invention is preferably applicable, for example, to apparatuses for producing semiconductor devices, such as exposure apparatuses and laser repair apparatuses, laser beam machining apparatuses, and lithography systems. The present invention also relates to a gas supply system and method for supplying mixed gases effectively to a plurality of gas laser sources.
2. Description of Related Art
The high power laser beam source includes a gas laser based on the use of a gas as a laser medium, which is used in a variety of fields. Especially, an excimer laser is known, in which a high power pulse laser beam is obtained. The high power pulse laser apparatus such as the excimer laser is used for the laser beam machining process and for the production process for semiconductor devices such as IC and LSI, especially for the lithography step.
The excimer laser, which is used for the applications as described above, uses a laser medium composed of a mixed gas comprising KrF (krypton fluoride) and ArF (argon fluoride). The excimer laser uses a mixture comprising several percent of Kr (krypton) and F.sub.2 (fluorine), or Ar (argon) and F.sub.2 (fluorine) respectively, and it uses Ne (neon) as a buffer gas. These components are proportionally mixed in an optimum mixing ratio in conformity with manufacturers of the laser. However, the mixing ratio changes while the laser is used. For this reason, in order to prolong the service life of the gas used for laser radiation and decrease the downtime during the gas exchange procedure by decreasing the amount of gas consumption, fluorine microinjection (F.sub.2 injection) has been hitherto performed especially for fluorine which has strong reactivity and which tends to decrease as a result of the reaction easily caused with metals, hydrogen, and carbon contained in the laser oscillator. Specifically, the fluorine microinjection is performed by injecting a two-component mixture, i.e., F.sub.2 /Ne (fluorine/neon).
Recently, the development has been further advanced, making it possible to decrease deterioration of the gas and prolong the service life of the laser. However, when the fluorine microinjection is performed, it is necessary that a part of the mixed gas contained in the laser beam source is once extracted, and then a minute amount of fluorine is injected, in order to avoid abnormal increase in internal pressure. Therefore, for example, in the case of the KrF excimer laser, the concentration of krypton (Kr) is decreased every time when the fluorine microinjection is performed, and it is necessary to simultaneously inject krypton (Kr) together with fluorine. Accordingly, the two-component mixture of F.sub.2 /Ne, which has been hitherto used for the fluorine microinjection, is changed to a three-component mixture of F.sub.2 /Kr/Ne (fluorine/krypton/neon) to perform the gas injection.
As for the laser such as the excimer laser based on the use of the mixed gas as the laser medium, the optimum mixing ratio (concentration) of the mixed gas used for the laser medium differs depending on the laser manufacturers. Even when the laser medium contains a common type gas such as F as in the mixed gas including KrF and ArF, the ratio of F is different when such a mixed gas is prepared. That is, the mixing ratio of Kr/F.sub.2 is mutually different from the mixing ratio of Ar/F.sub.2. For this reason, for example, in the case of the KrF laser, it is necessary to prepare a gas cylinder (tank) containing Kr, for example, Kr/Ne (krypton/neon) and a gas cylinder containing F.sub.2, for example, F.sub.2 /Ne, and it is necessary to provide any gas equipment for supplying the gases from the gas cylinders to the laser. Further, since the mixing ratio of Kr and F.sub.2 differs depending on the manufacturers, it has been hitherto necessary to provide any supply equipment corresponding to each of them. The same situation also arises in the case of the ArF laser.
As described above, when the lasers produced by different makers based on different laser media are used, the gas supply apparatus (gas supply equipment) including a plurality of gas cylinders and supply lines for supplying the gases has been hitherto installed for each of the lasers. Therefore, the conventional system is not effective in view of the space and the cost. Especially, in the case of fluorine, strict management is required, because it is a toxic gas. It is necessary to provide any gas supply equipment applicable to the toxic gas for each of the lasers, and hence an excessive management burden has been hitherto imposed.
It is forecasted, for example, that the lithography step carried out in the production of semiconductor devices or the like will, in the near future, highly possibly meet the necessity for the mix-and-match exposure for performing exposure by using, on an identical production line, an exposure apparatus (such as a stepper) based on the use of the KrF excimer laser and an exposure apparatus (such as a stepper) based on the use of the ArF excimer laser. In such a case, an inconvenience also arises in that an excessive installation space and an excessive cost are required, if the gas supply equipment applicable to the toxic gas is prepared for each of the exposure apparatuses as performed in the conventional system. It has been feared that such an inconvenience may cause a bottleneck when the mix-and-match exposure system is introduced.